Tag Archives: AL98

Invest 98L Brings Rain to South Texas

A low pressure system designated as Invest 98L brought rain to South Texas on Sunday morning. At 8:00 a.m. EDT on Sunday the center of Invest 98L was located at latitude 27.5°N and longitude 97.5°W which put it about 20 miles (30 km) south of Corpus Christi, Texas. Invest 98L was moving toward the west at 7 m.p.h. (11 km/h). The maximum sustained wind speed was 30 m.p.h. (50 km/h) and there were wind gusts to 40 m.p.h. (65 km/h). The minimum surface pressure was 1009 mb.

A low pressure system designated as Invest 98L brought rain to South Texas on Sunday morning when the center of the low moved inland just south of Corpus Christi. The low pressure system exhibited much more organization as it approached the coast. A distinct low level center of circulation was evident on both visible satellite and radar images. Bands of showers and thunderstorms were revolving around the center of the low pressure system. The strongest winds were occurring in bands in the eastern side of Invest 98L, which were still over the Gulf of Mexico.

Invest 98L will move around the southern side of a high pressure system over the southern U.S. The high pressure system will steer Invest 98L toward the west during the next several days. On its anticipated track Invest 98L will move inland over the Lower Rio Grande Valley. Invest 98L will drop widespread rain over South Texas. Many places could receive 2 to 4 inches (50 to 100 mm). Heavier rain could fall over some locations and localized flooding is possible. The National Weather Service Forecast Office in Brownsville, Texas issued a Flood Advisory for Jim Wells, Kleeburg and Nueces counties.

Potential Tropical Development Near East Coast of U.S.

There is the potential for the development of a tropical cyclone near the East Coast of the U.S. during the next several days.  A low pressure system, currently designated as Invest 98L developed over the northern Gulf of Mexico during the weekend.  The low moved slowly toward the northeast across the southeastern U.S.  At 2:00 a.m. EDT on Wednesday the low level center of Invest 98L was located at latitude 33.3°N and longitude 80.5°W which put it about 25 miles (40 km) west of Charleston, South Carolina.  The low was moving toward the east at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 25 m.p.h. (40 km/h) and there were wind gusts to 35 m.p.h. (55 km/h).  The minimum surface pressure was 1013 mb.

Invest 98L currently consists primarily of a lower level circulation.  Much of the circulation is over land and the center is west of Charleston, South Carolina.  Many of the bands revolving around the center of the low pressure system consist of showers and lower clouds.  There are bands of showers and thunderstorms on the far eastern edge of the circulation which is over the Gulf Stream.  An upper level trough over the southeastern U.S. is producing westerly winds which are blowing across the top of the low level circulation.

Invest 98L will move into an environment more favorable for the development of a tropical cyclone.  It will move over water where the Sea Surface Temperature is near 27°C when the center moves over the Atlantic Ocean.  The upper level trough will over the southeastern U.S. will cause moderate vertical wind shear.  The wind shear will inhibit development.  If thunderstorms develop closer to the center of circulation, those storms could cause the circulation grow vertically into the middle and upper troposphere.  If the thunderstorms release enough latent energy in the middle and upper troposphere, a warm core could form and Invest 98L could become a tropical cyclone.

The National Hurricane Center indicated in the 8:00 a.m. EDT Tropical Weather Outlook on Wednesday that the probability was 70% that a tropical or subtropical cyclone could form during the next five days.  An upper level trough approaching the eastern U.S. will steer the low pressure system toward the north-northeast during the next few days.  On its anticipated track the low pressure system will move near the East Coast of the U.S.  A reconnaissance aircraft is tentatively scheduled to investigate Invest 98L later on Wednesday, if necessary.

Non-Tropical Low Forms Over Northeast Gulf of Mexico

A non-tropical low pressure system formed over the northeastern Gulf of Mexico on Sunday.  The low pressure system is currently designated as Invest 98L.  At 2:00 p.m. EDT on Sunday the center of Invest 98L was located at latitude 28.4°N and longitude 85.5°W which put it about 100 miles (160 km) south-southwest of Apalachicola, Florida.  It was moving toward the east at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1009 mb.

The low pressure system formed along a frontal boundary that stalled over the northeastern Gulf of Mexico.  It is not usual for low pressure systems to form along stationary fronts.  A source of positive vorticity to provide counterclockwise rotation and upper level divergence to pump away mass and allow the surface pressure to decrease will generate a surface low.  The low pressure system does not have a warm core in the middle and upper levels and it is still associated with a frontal system.  So, it is classified as a non-tropical low pressure system.

The low pressure system will be moving through an environment that will be only marginally favorable for a transition to a tropical or subtropical cyclone.  The Sea Surface Temperature in the northeastern Gulf of Mexico is near 30°C.  So, there is plenty of energy to support the formation of a tropical cyclone.  However, an upper level ridge over the central U.S. and a trough over the northeastern U.S. are combining to produce northerly winds of 40 m.p.h. (65 km/h) over the northeastern Gulf of Mexico.  Those winds are generating significant vertical wind shear.  The shear has limited the development of thunderstorms in the northern half of the low and it may be tilting the vertical structure of the low toward the south.  The strong upper level winds will also inhibit divergence on the northern side of the low and they could make it difficult for a warm core to develop in the middle and upper levels.  The air north of the frontal boundary is drier continental air, which is another a negative factor for transition to a tropical cyclone.  Based on all of the environmental factors the National Hurricane Center is indicating that there is a 30% chance the low could make a transition to a tropical or subtropical cyclone.

The low pressure system is moving a little to the south of due east.  A strong surface high pressure system over the eastern U.S. is now pushing the front toward the south as a cold front.  The low is moving slowly eastward along the front.  Combination of the southward motion of the front and eastward motion of the low produces a forecast motion of a little south of due east.  On its anticipated track the low pressure system could reach the west coast of Florida in 24 to 36 hours.  So, the low has about a day, if it is going to transition to a tropical cyclone over the Gulf of Mexico.